The following patents have been considered in the preparation of this application: U.S. Pat. No. 2,860,311,
U.S. Pat. No. 3,907,336
U.S. Pat. No. 4,380,168
U.S. Pat. No. 4,420,970
U.K. No. 854,189
U.K. No. 2,023,296
GER. No. 227,590
GER. No. 1,193,000
GER. No. 1,234,163.
In general these patents reveal the need for two-walled or double wall piping in a wide variety of circumstances including the need to contain hazardous chemicals, the need to confine excessive pressures, and the need to maintain a predetermined condition of pressure or atmosphere. In all such needs what is provided is a first pipe wall and a second pipe wall. As shown in the prior art, it is conventional to take a pair of different diameter tubular pipe sections and to support them at their junctions by a fitting. The need to adequately seal the fitting is addressed in a number of these patents. It is indisputable that the use of a fitting multiplies the sealing problems since typically each pipe section is separately sealed to the fitting, this means the inner and outer pipe sections must be separately joined to the fitting, and not uncommonly the design of the fitting is two-piece, necessitating another seal.